Silver halide photographic emulsions sensitized by polyalkylene glycols



Patented July 8, 1947 SILVER HALIDE PHOTOGRAPHIC EMUL- SHONS SENSITIZED BY GLYCOLS POLYALKYLENE Ralph Kingsley Blake, Parlin, William Alexander Stanton,

New Brunswick, and Ferdinand Schulze, Westfield, N. J., assignors to E. I. du Pont de Nemours & Company, Wilmington, Del, a corporation of Delaware No Drawing Application January 10, 1945, Serial No. 572,248

Qlaims.

This invention relates to radiation-sensitive phototgraphic elements and more particularly to such elements sensitized by means of polyglycols. Still more particularly it relates to photographic elements having light-sensitive colloid-silver halide layers sensitized by means of polyglycols having a molecular weight of at least 400.

An object of this invention is to provide new means for increasing the phototonic character of photographic emulsions. A more specific object is to increase the speed and/or contrast of photographic silver halide emulsion layers. A further object is to provide photographic silver halide emulsions and emulsion layers of enhanced speedstability upon aging. A still further object is to provide such emulsions which have good coating qualities. Still other objects will be apparent from the following description of the invention.

It has been found that the phototonic character of colloid-silver halide emulsions and emulsion layers can be enhanced by bringing into operative contact therewith, a small amount of a higher polyglycol having a molecular weight of at least 400. This may advantageously be accomplished by incorporating such polyglycols with the emulsions prior to coating or they may be brought into operative association with an emulsion layer after coating. Thus, a silver halide emulsion layer may be impregnated or coated with a solution containing the aforedescribed polyglycols. Alternatively the polyglycols can be placed in a substratum coating or in an overcoating which is in operative contact with the emulsion layer.

The foregoin objects are attained in accordance with the preferred aspect of the invention by the use of the higher polyethylene glycols having a molecular weight of at least 400 and especially those having a molecular weight or an average molecular weight of at least 1500.

The aforesaid polyglycols may be added to the emulsions or brought into association with emulsion layersby dissolving them in water or watersolvent mixtures or in organic solvents which do not have a deleterious effect on' silver halide emulsions and adding the solution to an emulsion or coating composition.

The polyglycols described above are known chemical compounds and many of them are available commercially. They can be prepared in various ways, for example, by the removal of water from glycols and by the reaction of oxides with glycols. The reactions are generally carried out until the products have a molecular weight or an average molecular weight in excess of 400. Ethylene oxide, propylene .oxide-l-2, and -1,3

and butylene oxides-1,2 can be used in the preparation of the products and they may be reacted with ethylene glycol, diethylene glycol, etc. Their preparation is described in The Chemistry of Synthetic Resins, pages 990-994, published by Rheinhold Publishing Corporation (1935).

The preferred aspect of the invention involves sensitizing silver halide-colloid emulsions or emulsion layers with one or more'compounds of the formula:

I-IOCI-IzCHzO (CHzCHzO) nCH2CH2OH where n is '7 to 200 or more. Compounds having such a formula include nonaethylene glycol, decaethylene glycol, dodecaethylene glycol and higher homologues containing from 9 to 200 CH2CH2O groups. The lower members of the class are viscous liquids to semi-solids and.

solids, at 20 C., which are somewhat hygroscopic up to a molecular weight in excess of 1500. The higher homologues are waxy solids and as their moleclular weight increases to 4000 they become non-hygroscopic in character. The lower members of the series are easily soluble in water, the solubility becoming less as the molecular weights of the compounds increase. In general, the higher members of the series cannot be too easily isolated as single chemical entities. Instead, the condensation reaction leading to their preparation is carried to a point where the bulk of the material will consist of homologous compounds of similar chain length. Mixtures of two or more polyalkylene glycols or polyoxyalkylene glycols are selected on the basis of average molecular weight. Since a, difference of one or two ethylene oxide links in polymers of considerable chain length has a negligible effect on their physical and chemical properties, such mixtures can be readily employed in the present invention. For the purposes of this invention, it is sufficient to know the average molecular weight of the material to be used, and the fact that it may in all likelihood consist of a mixture of several compounds of closely. similar molecular weights does not reduce its effectiveness.

It has been discovered that the afore-described polyalkylene glycols are capable of increasing the sensitivity of photographic emulsions equally throughout the whole range of the spectrum in a manner analogous to the so-called sulfur sensitizers such as allyl-thioureas, thiocyanates, so-

. dium thiosulfate and sodium hyposulfite, yet they differ widelyin constitution and properties from such compounds. The polyglycols, moreover, may be used in conjunction with such sulfur sensitizers and have a beneficial effect on the resulting emulsion.

The polyglycols are especially effective with light of various wavelengths. Prominent among the compounds used for this purpose have been the cyanine and merocyanine dyes representative" types of which are described in .United .StatesPatents 2,010,388, 2,079,376, 2,202,990, 2,202,991, 2,202,992, 2,278,461, and 2,265,908.

The invention will be further illustrated in the following examples.

Example-I A gelatino-silver-halide "emulsion :containing 6.8% silver iodide and 93.2% silver bromide was brought to its maximum lightsensitivity in condition for pouring, The followin quantities of polyethylene glycols of the indicated average molecular weights were added to samples of the above-described emulsion each containing about 0.15 molof'silveri-halides. The resulting emulsion samples were coatedon cellulose nitrate film base ina thin layer and dried. :Samples of said film elements were then exposed .in a'type -IIB Sensitom'ete'r, developed in a developerof the following composition N-methyl-para-aminophenolsulfate 7 grams 0.8 Hydroquinone 'do. 1.0 Sodiumsulfite (anhydrous) do 90.0 Borax -do 3.0 Potassium bromide do 0.1 Water to -li-ter 1 .for 7 minutes .at 68 'F. withthe results listed in the following table.

Molecular Weight of 1 Relative Compound Quantlty Speed Gamma Fog .EmampleII known to the art.

Example I II A gelatino-silver-halide emulsion containing 6.8% silver iodide and 93.2% silver bromide was coated on cellulose nitrate film base in a manner After the coating had been suitably dried, an aqueous gelatin solution containing 25.6 grams of gelatin per liter and .097 g. of a polyethylene glycol with an average molecularweight of 7200 was coated thereon as an antiabrasionlayer. The resulting film element, after drying. was exposed and processed in the manner described .in Example I. The element described A slow,- gelatino-silver-halide emulsion containing 1% silver iodide and 99% silver bromide was modified bythe addition-of 0.5 g. of a polyethylene glycol having an average molecular weight of 7200 for each 0.15 mol of silver halide. The resulting emulsion was then coated on cellulose nitrate film base and dried in the manner known to the art. Over this emulsion there was then coated a fast iodo-bromide emulsion containing 6.6% silver iodide and 93.2% silver bromide. After 'development,'washing and drying as in ExampleI, sensitometric evaluation of this two layer emulsion combination as compared with a similar combination containing no added material in 'the uridercoat showed the following improvement in speed for both fresh and aging tests.

A gelatino silver-halide emulsion containing 6.8% silver-iodide and 93.2% silver bromide was brought to its maximum light sensitivity, "ready for pouring. To'samples ,containing'0.-l5 mol of silver halide, the following quantities of 'a poly- Sodium sulfite grams 30 Paraformaldehyde 'do 7.5 Potassium metabisulfite do 2.5 Boric'acid, crystals do 7.5 Hydroquinone 'd'o 22.5 Potassium bromide do 1.5 Wate'r'tm liter '1 Evaluation 'of the -coa'tedemulsions showed a 'sig nificant increase ineffective contrast.

.Molecular Weight of Compound Quantity ggggggg .Fog

(0) Control 3:75 :01 4l4. 1.0.m1 4.64 ..,()1

(c) Goritrol 4. 30 01 4141""; O.5H1l 4.87 ..O].

ethylene glycol of approximately 7200 molecular weight were added. The emulsion samples were then coated as described in Example I and eX- posed and processed inan identical'manner. The results obtained .are .set forth in the following table:

seer R 0 ye y e a we one Glycol Speed Gamma Fug Added Grams 1 Not only 'do the compound of the present invention increase the over-all speed of photographic emulsions, but in addition they improve the aging characteristics of emulsions. For example,.they improve the speed of afilm-element exposed to accelerated aging conditions even beyond the improvement exhibited by normally aged films. This effect is demonstrated in the following example.

Example VI The following tests were carried out on samples of emulsion exactly as. described in Example I. After drying the samples were exposed, processed and evaluated according to the procedure of that example. The following results were obtained:

Molecular Weight of Polyethylene Glycol Added Age of Coating When Developed Relative Speed Fog Gamma Fresh 1 Week 1 Week at 120. Fresh 1 Week 1 Week at 120. Fresh 1 Week 1 Week at 120.

Example VII A gelatino-silver halide emulsion containing about 9.6 silver iodide and 90.4% silver bromide of the type used for cinematographic taking film was brought to its maximum light sensitivity and prepared for coating. The following quantities of polyethylene glycols based on 0.15 mols of silver halide were added to molten samples of this emulsion and the samples coated on a cellulose nitrate film base and the resultin film elements dried in the usual fashion. The resulting coated elements were exposed to a series of graduated light intensities on an intensity scale sensitometer (type 1A) and then processed in the manner described in Example I except that the time of development in this case was increased by 3 minutes. The following results were obtained:

Average Molecular Wt. of Compound Quantity Added Fog Example VIII I 7200 average molecular weight based on .075 mol of silverhalide. The other received no additional treatment. Both samples were coated on heavy white baryta-coated paper and dried in warm dry air. Both samples were then exposed on a sector-wheel type of sensitometer, developed in a standard paper developer, fixed, washed and dried in the manner known to the art. Reflection densities were then read on a combination transmission-reflection densitometer of the type devised by Morrison and McFarlane (J. 0. S. A. 25 (417 1935). The results indicated that the polyethylene glycol treated coating had a relative speed 32% greater than that of the untreated control. I

As described in the preceding examplesthe polyalkylene glycols of the present invention can be incorporated with the emulsion prior to coating or brought into contact therewith after coating. Thus a silver halide emulsion can be impregnated with a solution containing the compounds or the polyalkylene glycols can be placed in a sub-stratum coating or in an overcoating in intimate contact with the emulsion layer. The compounds can be added to the emulsion or to adjacent coatings from aqueous solution or from an organic solvent. Most of the compounds are sufficiently water-soluble to be utilized from aqueous solution, other useful solvents include watermiscible solvents, e. g., ethanol, methanol, acetone, dioxane, etc. which can be mixed with water.

This invention is not limited to the use of gelatin as the binding agent for the silver halides. On the contrary, other h'ydrophilic colloids can be used. Suitable colloids include agar-agar, polyglycuronic acids, zein, collodion, water-soluble cellulose derivatives such as substantially hydrolyzed cellulose acetate, cellulose esters of hydroxy monocarboxylic acids, e. g., lactic or glycolic acids, alkali metal salts of cellulose esters of dicarboxylic acids such as phthalic acid, polyvinyl alcohol, partially hydrolyzed polyvinyl acetate and interpolymers thereof with unsaturated materials such as styrene, maleic acid, etc., water-soluble polyvinyl acetals and other hydrophilic synthetic or natural resins and polymeric compounds. Suitable hydrophilic colloids of the above types are described in United States Pat.- ents- 2,110,491, 2,276,322, 2,276,323, 2,286,215, and 2,211,323.

The polyglycols hereof may be added to the hydrophilic colloid silver halide emulsion over a wide range of proportions, e. g., from 1 part of polyglycol in 350,000 parts of emulsion to 1 part of polyglycol in 12 parts of emulsion. The amount of sensitizing effect obtained depends to some extent upon the molecular weight of the particular compound or compounds employed and upon the concentration which must be used. In general, the higher the molecular weight of the compound the lower the concentration which must -be used to give the optimum efi'ect.

An advantage of this invention reside in the fact that the enhanced phototonic character (viz. state of sensitiveness to light) of photographic emulsions can be attained in a simple and economical manner. A further advantage is that commercially available products are used. Another advantage is that the polyglycols may be used with color formers, sensitizing dyes, fog inhibitors, etc. without having any deleteriou effect thereon.

We claim:

1. In a photographic element a light-sensitive silver halide emulsion layer having in intimate contact therewith a polyalkylene glycol having a 7 molecular weight of at least 400 the alkylene groups of which contain 2 to 4 carbon atoms and constitute the only hydrocarbon groups in the said glycols.

2. In a photographic element a light-sensitive halide emulsion layer which contains polyalkylene glycol having a molecular weight of at least 400 the alkyl'ene groups of which contain 2 to 4 carbon atoms and constitute the only hydrocarbon groups in the said glycols.

3. In a photographic'element a light-sensitive silver halide emulsion layer having in intimate contact therewith a polyethylene glycol having a molecular weight of at least 400 and wherein the ethylene groups constitute the only hydrocarbon groups of the said glycols.

4. In a photographic element a light-sensitive silver halide emulsion layer which contains a polyethylene glycol having a molecular Weight of at least 400 and wherein the ethylene groups constitute the only hydrocarbon groups of the said glycols.

5. A photographic element comprising a support, a light-sensitive silver halide emulsion layer containing a polyethylene glycol having a molecular Weight from 400 to 8000 and wherein the ethylen groups constitute the only hydrocarbon groups of the said glycols.

RALPH KINGSLEY BLAKE. WILLIAM ALEXANDER STANTON. FERDINAND SCHULZE.

REFERENCES CITED The following references are of record in the file of this patent:

Certificate of Correction Patent No. 2,423,549. July 8, 1947.

RALPH KINGSLEY BLAKE ET AL.

It is hereby certified that errors appear in the printed specification of the above numbered patent requiring correction as follows: Column 1 line 2, for phototgraphic read photographic; column 2, line 18', formoleclular read molecular; column 7, line 6, claim 2, before the word halide insert silver; and that the said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent Ofiice.

Signed and sealed this 27th day of April, A. D. 1948.

THOMAS F. MURPHY,

Assistant Uommiasioner of Patents. 

